868 On the Temperature of Sublimation, 



Tellurium. 



Tellurium gives upon the apophorometer two sublimates 

 as stated in my first paper (loo. cit.) : a black low-temperature 

 sublimate of TeO and a white high-temperature sublimate of 

 Te0 2 . If a little of the black sublimate be scraped from the 

 glass and placed upon the hob, it will be found to melt at 

 about 570° and either to resublime at once as a black sublimate 

 or to again partly solidify on the hob, slowly whiten, melt 

 again at about 850° and, at or near this temperature, volatilize 

 on to the watch-glass as the white sublimate Te0 2 . If a little 

 of the white sublimate is placed directly on the hob and 

 slowly heated from a low temperature it will blacken at a 

 temperature below 500°, reverting to TeO. Rapidly heated 

 it melts as above and sublimes at about 850°. The recognition 

 of these sublimates is easy. 



I have examined only 7 tellarides. They appear to indicate 

 that the tellurides will be found divisible into groups according 

 as the molecule is of the structure RTe or RTe 2 . But, of 

 course, the evidence is too slender to justify discussion. 



Table IV. 

 RTe. 



t°. 

 850 

 Hessite. Ag 2 Te. Altai. TeO? Te0 2 900 



Altaite. PbTe. Las Craces. TeO? Te0 2 850 



RTe : K Q Te 3 : Te. 



Calaverite. (AuAg)Te,. " TeO... 530 



Te0 2 600 



' Petzite ' (?). Contains over 60 per cent, of Te. TeO 460 



Te0 2 900 



Tetradymite. Bi 2 Te 3 . Hungary. TeO 460 



Te0 2 750 



Nagyagite. Au Pb u Sb 3 Te 7 S 17 . Nagyag. TeO 525 



Te0 2 610 



Tellurium. Te. Loc. TeO 525 



Te0 2 850 



It will be noticed that there is a readily observed dis- 

 tinguishing feature in the case of the two indicated groups 

 of tellurides : the presence or absence of the black sublimate. 

 This, of course, is explained by the fact that in the one group 

 the temperature of decomposition is too high for the equi- 

 librium of the molecule TeO. 



